This invention relates to orthodontic appliances, and particularly to an appliance for orthopedic treatment of the jaw bones to correct Class III malocclusion.
As illustrated in FIG. 1, human jaw bones comprise an upper jaw bone or maxilla 10 and a lower jaw bone or mandible 20, both pivotally linked for interrelated movement. An upper set of teeth 11 and a lower set of teeth 21 are formed on the respective jaw bones. Generally, as shown in FIG. 9, maxilla 110 is protracted a certain distance (B) anteriorly to mandible 120. A malocclusion where maxilla 10 is positioned posteriorly to mandible 11 a certain distance (A) as shown in FIG. 1 is classified as "Skeletal Class III Malocclusion."
The Skeletal Class III Malocclusion is caused by a relative undergrowth of maxilla 10 or overgrowth of mandible 20 or a combination of both. Orthopedic surgical treatment is applied for adults having excessive malocclusion while a camouflage treatment is available for a mild case. For children still growing, chin capsets restraining mandibular growth or traction devices protracting the maxilla are used for correcting malocclusion. The traction devices are designed for correcting discordance of jaw bones by restraining mandibular growth while inducing maxillary growth forward. Therefore, a traction device works most effectively in childhood when the maxilla actively grows causing high migration to the front.
FIG. 2 illustrates an embodiment of a known chin capset which comprises a head cap 1, chin cap 2 and traction bands 3 such as rubber bands to draw the chin cap back in the direction indicated by the arrow. FIG. 3 illustrates a known chin capset comprising a head cap 1, chin cap 2, traction bands 3 and forward-pulling bars 4 which pulls the maxilla forward relative to the mandible. Extraorally revealed head caps 1 and chin caps 2 make the chin capsets distracting and embarrassing for patients as well as inherently inconvenient to wear.
FIGS. 4 and 5 show an example of a maxilla traction device which was disclosed in Japanese Patent Publication No. 61-47098. This device comprises a cylinder 30 housing a spring (not shown), a movable rod 31 which linearly moves compressing the spring, a fixing rod 32 pivotally linked to an end of the cylinder 30, a first connector 34 pivotally linked at one of the movable rod 31 and united with a mandibular tooth 22, and a second connector 35 pivotally linked to an end of the fixing rod 32 and united with a maxillary tooth 12. This maxilla traction device is mounted on a maxillary tooth 12 and a mandibular tooth 22 and works to promote maxillary growth while restraining mandibular growth. Unlike the chin capset, it is mounted intraorally and therefore is more acceptable to patients. However, the maxilla traction device still has drawbacks. First, as first and second connectors 34 and 35 are mounted on a single maxillary and mandibular teeth respectively, the traction force is likely to be concentrated on the tooth causing damage on it. Therefore, another treatment is likely to be required after correcting the malocclusion. Second, its construction makes it inconvenient for a patient to put the device on and take it off for cleaning.
Other examples of orthodontic devices for correcting malocclusion are found in the following patents:
______________________________________ Pat. No. Inventor Issue Date ______________________________________ 3,798,773 Northcutt Mar. 25, 1974 4,619,609 Clark Oct. 28, 1986 4,708,646 Jasper Nov. 24, 1987 5,120,218 Hanson Jun. 9, 1992 5,352,116 West Oct. 4, 1994 ______________________________________
FIG. 7 of U.S. Pat. No. 4,708,646 to Jasper illustrates the use of a pushing force for correction of underbite, and FIG. 8 of that patent illustrates the use of a pushing force bet ween two splints for the correction of overbite. A device of the type shown in FIG. 8 has been made with acrylic molded over an impression of a patient's teeth so as to form a rigid splint conducive to a snap fit onto the patient's teeth. This device is ordinarily secured to the patient's teeth with a bonding agent applied by the patient's orthodontist.
U.S. Pat. No. 4,619,609 to Clark discloses a facebow having an inner bow and an outer bow and a forwardly projecting labial hook secured thereto for combined extraoral and intermaxillary traction, and also discloses complementary upper and lower bite blocks with angled pressure surfaces. Treatment of Class II malocclusion with the traction mechanism and/or bite blocks is described in some detail, and bite blocks having oppositely directed pressure surfaces to those described for Class II treatment are mentioned for the treatment of selected Class III malocclusions. The disclosed facebow's outer bow extends outside the patient's cheeks, where it is attached to headgear worn by the patient.
Retention of bite blocks can be problematic with traction applied, as noted by Clark in Twin Block Functional Therapy (Mosby-Wolfe, 1995), on page 134. In a chapter of that book devoted to the treatment of Class III malocclusion, Clark suggests a reverse pull facial mask for use with reverse Twin Blocks to apply an additional component of orthopedic force to advance the maxilla. Unlike the facebow of the Clark patent and a similar facebow discussed elsewhere in the Clark book in the context of Class II malocclusion, the reverse pull facial mask has no inner bow; elastic traction is applied only between the upper Twin Block and an extraoral bowed bar spanning the width of the patient's face. That bar and the outer bow of the Clark patent are highly visible and are aesthetically and otherwise undesirable to many patients, particularly as used with the necessary supporting headgear.
It is a general object of the present invention to provide improved methods and devices for treating Class III malocclusion.
It is another object of the present invention to provide an improved Class III orthodontic appliance which is intraorally mountable and thus less noticeable, consequently more acceptable to the patient, and ultimately more conducive to proper wear and desired results.
Another object of the present invention is to provide an improved Class III appliance which produces uniform traction force to the sets of teeth on the upper and lower jaws.
It is still another object of the present invention to provide a Class III appliance which is easy for a patient to put on and take off.